1. Field of the Invention
This invention relates to mobile communication systems that are configured by mobile stations (or mobile terminals) and radio base stations, and particularly to traffic collection and control methods employed for radio base station control devices for controlling the radio base stations. This application is based on patent application No. Hei 9-152734 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
According to the conventional traffic control method of the mobile communication system, there is provided a threshold value which is subjected to xe2x80x9chandoffxe2x80x9d to or from a certain base station. For example, the conventional method controls call a quantity (or number of calls) of the base station, at which a number of calls concentrate, by changing its threshold value. An example of the above method is disclosed by the paper of Japanese Patent Application, Publication No. Hei 6-164477.
Now, the above control method will be described in conjunction with FIG. 9. FIG. 9 shows an example of the mobile communication system that contains a mobile telephone exchange 4, a first radio base station 5, a second radio base station 6 and a mobile terminal 7. Consider a case where a communication channel utilization rate xcex1 of the first radio base station 5, which acts as a handoff source, is less than a prescribed threshold value, while a communication channel utilization rate xcex2 of the second radio base station 6, which acts as a handoff destination, is greater than (or equal to) the prescribed threshold value. In such a case, a threshold value xcex94AB is provided as a handoff condition and is used for making a decision with respect to a receiving level difference between a first receiving level, which is detected between the first radio base station 5 and the mobile terminal 7 located in proximity to the handoff source, and a second receiving level which is detected between the second radio base station 6 and the mobile terminal 7. This threshold value xcex94AB is corrected by a value X, which is calculated based on the communication channel utilization rates xcex1 and xcex2, so the corrected one is used as a new threshold value xe2x80x9cxcex94+Xxe2x80x9d. Incidentally, a reference symbol A designates an area (or base station area) set for the first radio base station 5, B designates an area (or base station area) set for the second radio base station 6. In addition, xcex94AB designates the threshold value for the receiving level difference calculated in connection with a direction from the first radio base station 5 to the second radio base station 6, while xcex94BA designates a threshold value for a receiving level difference calculated in connection with an inverse direction.
According to the aforementioned traffic control method which is conventionally known, controlling of traffic quantity of the base station area is performed by controlling the hand-over of the mobile terminal. So, it is not possible to reduce the traffic quantity of the base station based on where the mobile terminal is located unless the mobile terminal moves from the base station area corresponding to a hand-over source to the base station area corresponding to a hand-over destination.
In the aforementioned traffic control method, mobile terminals concentrate at the area of the base station where the handoff is performed. For this reason, if a number of the mobile terminals temporarily reaches a prescribed number of mobile terminals for which the base station allows communications, a mobile terminal which is over the prescribed number of mobile terminals cannot send or receive a call.
It is an object of the invention to provide a mobile communication system with traffic collection and control for radio base stations, which is capable of reducing a number of call failure events due to shortage of communication lines of the radio base station and which is capable of effectively using the radio resource.
A mobile communication system of this invention is established using a mobile terminal, base stations and a base station control device. Herein, each of the base stations having respective areas for mobile communication services thereof is capable of relaying conversation, made by the mobile terminal, by radio communication. The base station control device observes (or monitors) traffic (i.e., number of calls in progress) with respect to each of the base stations. In response to a conversation start event or a conversation end event that takes place in the mobile terminal which is located in an area of a base station whose traffic is large, the base station control device searches a surrounding base station whose traffic is relatively small. For management of the statuses of the base stations, the base station control device provides a table storing a number of calls in progress as well as a list of surrounding base stations with respect to each of the base stations.
The base station control device controls an area of the searched base station to enable radio communication with respect to the mobile terminal. For example, output of the searched base station is increased so that an area of the searched base station is broadened to cover location of the mobile terminal.
Thus, it is possible to provide uniform call connection service. In addition, it is possible to avoid occurrence of call failure due to shortage of communication lines, so it is possible to effectively use radio resources.